Check
the 'Private Post Only' to allow only admin to view this post.
Meanwhile, uncheck 'Show' option to hide it from public viewing and
select guestbook 'Status' as 'Approve' or 'Pending as you wish.

(Note:
Please note that, if you have selected 'Private Post Only' which means
that your post is viewable by admin only and it will not display at your
front end even if you check 'Show' option.)

Click
on 'Update' button once you're done or click on 'Delete' button to
remove particular post right away. Use a navigator to help you edit the
following guestbook and click on 'View Comment' located on the top right
to view visitor comments for particular guestbook.